小白学c++之多线程互斥锁

#include <stdio.h>#include <stdlib.h>#include <pthread.h>#include <unistd.h>pthread_mutex_t lock;int ticketcount=5;void* salewinds1(void* args){while(1){pthread_mutex_lock(&lock);if(ticketcount>0){printf("window1 start %d\n",ticketcount);sleep(1);ticketcount--;printf("sale ticket finish:%d\n",ticketcount);}else{pthread_mutex_unlock(&lock);//这句如果不加会造成程序死锁pthread_exit(NULL);}pthread_mutex_unlock(&lock);sleep(1);}return NULL;}void* salewinds2(void* args){while(1){pthread_mutex_lock(&lock);if(ticketcount>0){printf("window2 start:%d\n",ticketcount);sleep(1);ticketcount--;printf("sale finish:%d\n",ticketcount);}else{pthread_mutex_unlock(&lock);//这句如果不加会造成程序死锁pthread_exit(NULL);}pthread_mutex_unlock(&lock);sleep(1);}return NULL;}int main(int argc,const char* argv[]){pthread_t thd1;pthread_t thd2;int val1=1;int val2=2;pthread_mutex_init(&lock,NULL);pthread_create(&thd1,NULL,salewinds1,NULL);pthread_create(&thd2,NULL,salewinds2,NULL);pthread_join(thd1,(void**)&val1);pthread_join(thd2,(void**)&val2);printf("val1:%d....val2:%d\n",val1,val2);pthread_mutex_destroy(&lock);return 0;}

如果一个线程被加锁，一定要在线程退出前解锁，否则不解锁的线程不会执行pthread_exit，除非使用exit直接终止进程。

#include <stdio.h>#include <stdlib.h>#include <pthread.h>#include <unistd.h>pthread_mutex_t lock;int ticketcount=5;void* salewinds1(void* args){while(1){pthread_mutex_lock(&lock);if(ticketcount>0){printf("window1 start %d\n",ticketcount);sleep(1);ticketcount--;printf("sale ticket finish:%d\n",ticketcount);}else{pthread_mutex_unlock(&lock);//这句如果不加会造成程序死锁pthread_exit(NULL);}pthread_mutex_unlock(&lock);sleep(1);}return NULL;}void* salewinds2(void* args){while(1){pthread_mutex_lock(&lock);if(ticketcount>0){printf("window2 start:%d\n",ticketcount);sleep(1);ticketcount--;printf("sale finish:%d\n",ticketcount);}else{//pthread_mutex_unlock(&lock);//这句如果不加会造成程序死锁//pthread_exit(NULL);exit(1);}pthread_mutex_unlock(&lock);sleep(1);}return NULL;}int main(int argc,const char* argv[]){pthread_t thd1;pthread_t thd2;int val1=1;int val2=2;pthread_mutex_init(&lock,NULL);pthread_create(&thd1,NULL,salewinds1,NULL);pthread_create(&thd2,NULL,salewinds2,NULL);pthread_join(thd1,(void**)&val1);pthread_join(thd2,(void**)&val2);printf("val1:%d....val2:%d\n",val1,val2);pthread_mutex_destroy(&lock);return 0;}

可以正常退出。

</pre><pre name="code" class="cpp">

#include <stdio.h>#include <stdlib.h>#include <pthread.h>#include <unistd.h>pthread_mutex_t lock;int ticketcount=5;void* salewinds1(void* args){while(1){pthread_mutex_lock(&lock);if(ticketcount>0){printf("window1 start %d\n",ticketcount);sleep(1);ticketcount--;printf("sale ticket finish:%d\n",ticketcount);}else{//pthread_mutex_unlock(&lock);//这句如果不加会造成程序死锁//pthread_exit(NULL);//exit(1);return NULL;}pthread_mutex_unlock(&lock);sleep(1);}return NULL;}void* salewinds2(void* args){while(1){pthread_mutex_lock(&lock);if(ticketcount>0){printf("window2 start:%d\n",ticketcount);sleep(1);ticketcount--;printf("sale finish:%d\n",ticketcount);}else{//pthread_mutex_unlock(&lock);//这句如果不加会造成程序死锁//pthread_exit(NULL);//exit(1);return NULL;}pthread_mutex_unlock(&lock);sleep(1);}return NULL;}int main(int argc,const char* argv[]){pthread_t thd1;pthread_t thd2;int val1=1;int val2=2;pthread_mutex_init(&lock,NULL);pthread_create(&thd1,NULL,salewinds1,NULL);pthread_create(&thd2,NULL,salewinds2,NULL);pthread_join(thd1,(void**)&val1);pthread_join(thd2,(void**)&val2);printf("val1:%d....val2:%d\n",val1,val2);pthread_mutex_destroy(&lock);return 0;}

不可以正常退出

#include <stdio.h>#include <stdlib.h>#include <pthread.h>#include <unistd.h>pthread_mutex_t lock;int ticketcount=5;void* salewinds1(void* args){while(1){pthread_mutex_lock(&lock);if(ticketcount>0){printf("window1 start %d\n",ticketcount);sleep(1);ticketcount--;printf("sale ticket finish:%d\n",ticketcount);}else{pthread_mutex_unlock(&lock);//这句如果不加会造成程序死锁//pthread_exit(NULL);//exit(1);return NULL;}pthread_mutex_unlock(&lock);sleep(1);}return NULL;}void* salewinds2(void* args){while(1){pthread_mutex_lock(&lock);if(ticketcount>0){printf("window2 start:%d\n",ticketcount);sleep(1);ticketcount--;printf("sale finish:%d\n",ticketcount);}else{//pthread_mutex_unlock(&lock);//这句如果不加会造成程序死锁//pthread_exit(NULL);//exit(1);return NULL;}pthread_mutex_unlock(&lock);sleep(1);}return NULL;}int main(int argc,const char* argv[]){pthread_t thd1;pthread_t thd2;int val1=1;int val2=2;pthread_mutex_init(&lock,NULL);pthread_create(&thd1,NULL,salewinds1,NULL);pthread_create(&thd2,NULL,salewinds2,NULL);pthread_join(thd1,(void**)&val1);pthread_join(thd2,(void**)&val2);printf("val1:%d....val2:%d\n",val1,val2);pthread_mutex_destroy(&lock);return 0;}

可以退出，有时也可能不会退出，跟加锁的位置有关